Light valves having an electro-optically active element comprising a liquid crystal composite are known. In a liquid crystal composite, plural volumes or droplets of a liquid crystal material are dispersed, encapsulated, embedded, or otherwise contained within a matrix material such as a polymer. Exemplary disclosures include Fergason, U.S. Pat. No. 4,435,047 (1984); West et al., U.S. Pat. No. 4,685,771 (1987); Pearlman, U.S. Pat. No. 4,992,201 (1991); Dainippon Ink, EP 0,313,053 (1989). These light valves may be used in displays and window or privacy panels.
The liquid crystal composite is disposed between transparent electrodes, which are respectively supported by substrates (e.g., glass or a transparent polymer). When no voltage is applied across the electrodes (the field-off state), incident light is substantially scattered and/or absorbed. When an appropriate voltage is applied across the electrodes (the field-on state), the liquid crystal composite changes its optical state to one in which incident light is substantially transmitted.
The liquid crystal composite may be applied onto an electrode (and, if the electrodes do not entirely covered substrate, also to uncovered portions of the substrate) as an emulsion in an aqueous carrier medium. The carrier medium is allowed to evaporate, and an opposing electrode and substrate are laminated on top of the liquid crystal composite to form the light valve. Sometimes the emulsion coats poorly onto the electrode-substrate combination, leading to irregular coatings, cratering, pin-holing, streaking, irregular thicknesses, and other defects. Poor light valve performance may result. The addition of surfactants to the emulsion prior to coating can lead to better quality coatings. However, prior art surfactants have been found to adversely affect the electrooptical characteristics of the liquid crystal composite, such as lowering the voltage holding ratio.
Thus, it is desirable to develop coating aids which lead to higher quality coatings but which do not adversely affect the electro-optical characteristics of the liquid crystal composite.